Stability of genomic DNA fragment patterns in methicillin resistant Staphylococcus aureus (MRSA) during the course of intra- and interhospital spread

Human-associated Staphylococcus aureus strains within great ape populations in Central Africa (Gabon)

The risk of serious infections caused by Staphylococcus aureus is well-known. However, most studies regarding the distribution of (clinically relevant) S. aureus among humans and animals took place in the western hemisphere and only limited data are available from (Central) Africa. In this context, recent studies focused on S. aureus strains in humans and primates, but the question of whether humans and monkeys share related S. aureus strains or may interchange strains remained largely unsolved. In this study we aimed to evaluate the distribution and spread of human-like S. aureus strains among great apes living in captivity. Therefore, a primate facility at the International Centre for Medical Research of Franceville (Gabon) was screened. We detected among the primates a common human S. aureus strain, belonging to the spa-type t148. It was isolated from three different individuals of the western lowland gorilla (Gorilla gorilla gorilla), of which one individual showed a large necrotizing wound. This animal died, most probably of a staphylococcal sepsis. Additionally, we discovered the t148 type among chimpanzees (Pan troglodytes) that were settled in the immediate neighbourhood of the infected gorillas. A detailed analysis by pulsed field gel electrophoresis showed that the gorilla and chimpanzee isolates represented two closely related strains. To our knowledge, this is the first report of a human-associated S. aureus strain causing disease in great apes. The simultaneous detection in gorillas and chimpanzees indicated an interspecies transmission of this S. aureus strain. Our results recommend that protection of wild animals must not only be based on habitat conservation, but also on the assessment of the risk of contact with human pathogens.

The role of healthcare personnel in the maintenance and spread of methicillin-resistant Staphylococcus aureus

Healthcare workers may acquire methicillin-resistant Staphylococcus aureus (MRSA) from patients, both hospital and home environments, other healthcare workers, family and public acquaintances, and pets. There is a consensus of case reports and series which now strongly support the role for MRSA-carrying healthcare personnel to serve as a reservoir and as a vehicle of spread within healthcare settings. Carriage may occur at a number of body sites and for short, intermediate, and long terms. A number of approaches have been taken to interrupt the linkage of staff-patient spread, but most emphasis has been placed on handwashing and the treatment of staff MRSA carriers. The importance of healthcare workers in transmission has been viewed with varying degrees of interest, and several logistical problems have arisen when healthcare worker screening is brought to the forefront. There is now considerable support for the screening and treatment of healthcare workers, but it is suggested that the intensity of any such approach must consider available resources, the nature of the outbreak, and the strength of epidemiological associations. The task of assessing healthcare personnel carriage in any context should be shaped with due regard to national and international guidelines, should be honed and practiced according to local needs and experience, and must be patient-oriented.

Epidemiology and clonality of methicillin-resistant and methicillin-susceptible Staphylococcus aureus causing bacteremia in a tertiary-care hospital in Spain

OBJECTIVES

To describe the relative proportions of nosocomial and community-onset Staphylococcus aureus bacteremia at our institution and the epidemiologic characteristics and clonal diversity of S. aureus isolates, as determined by pulsed-field gel electrophoresis (PFGE) and antimicrobial resistance patterns.

DESIGN

Retrospective cohort study of all cases of S. aureus bacteremia between October 2001 and October 2002.

SETTING

A 1300-bed, tertiary-care hospital.

RESULTS

One hundred sixty-two unique episodes of S. aureus bacteremia were identified. Forty-three cases (26.5%) were caused by methicillin-resistant S. aureus (MRSA). Most cases of S. aureus bacteremia, whether MRSA or methicillin susceptible (MSSA), were nosocomial in origin (77.2%) or were otherwise associated with the healthcare system (16%). Only 11 (6.8%) of the cases (all MSSA) were strictly community acquired. Thirty-five unique macrorestriction patterns were identified among the 154 isolates that were typed by PFGE. Four major genotypes were defined among the isolates of MRSA, with 36 (85.7%) represented by a single PFGE type. Of the isolates within this major clone, all (100%) were ciprofloxacin resistant and 77.8% were erythromycin resistant. In contrast, the 112 isolates of MSSA comprised 31 different PFGE types, 3 of which represented 42.9% of all MSSA isolates and were associated with both nosocomial and community-onset bacteremia.

CONCLUSIONS

Most cases of S. aureus bacteremia in our healthcare region are nosocomial in origin or are acquired through contact with the healthcare system and are thus potentially preventable. To preclude dissemination of pathogenic clones, it is therefore necessary to redouble preventive measures in both the hospital and the community.

Clonal spread of methicillin-resistant Staphylococcus aureus in a large geographic area of the United States

Methicillin resistance in Staphylococcus aureus has rapidly increased over the last two decades. This increase is paralleled by the emergence of unique multi-resistant MRSA clones. In Brazil, Argentina, Uruguay, Portugal and Czech Republic a specific MRSA clone is widely spread, the so-called Brazilian epidemic clone. Another epidemic clone, the Iberian clone, is disseminated in Spain, Portugal, Belgium, Scotland, Italy, Germany and New York. Thus, a large number of hospital-acquired infections have been caused by specific MRSA clones. Using different molecular techniques for MRSA typing, we verified that two unique epidemic clones are spread over large geographic area in the US. In addition, we showed that a previously described MRSA clone type, the New York clone (I::A:A), is widely spread beyond the New York frontiers.

An outbreak of pyodermas among neonates caused by ultrasound gel contaminated with methicillin-susceptible Staphylococcus aureus

OBJECTIVE

To investigate an outbreak of methicillin-susceptible Staphylococcus aureus (MSSA) infections in a neonatal clinic.

DESIGN

Prospective chart review, environmental sampling, and genotyping by two independent methods: pulsed-field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). A case-control study was performed with 31 controls from the same clinic.

SETTING

A German 1,350-bed tertiary-care teaching university hospital.

RESULTS

There was a significant increase in the incidence of pyodermas with MSSA; 10 neonates in good physical condition with no infection immediately after birth developed pyodermas. A shared spatula and ultrasound gel were the only identified infection sources. The gel contained MSSA and was used for hip joint sonographies in all neonates. PFGE and RAPD-PCR patterns from 6 neonates and from the gel were indistinguishable and thus genetically related clones. The case-control study revealed no significant risk factor with the exception of cesarean section (P=.006). The attack rate by days of hip-joint sonography between April 15 and April 27, 1994, was 11.8% to 40%.

CONCLUSIONS

Inappropriate hygienic measures in connection with lubricants during routine ultrasound scanning may lead to nosocomial S. aureus infections of the skin. To our knowledge this source of S. aureus infections has not previously been described.

A community pseudo-outbreak of invasive Staphylococcus aureus infection

Outbreaks of invasive infection caused by methicillin-susceptible and methicillin-resistant Staphylococcus aureus occur in hospitals, long term care institutions, and in patients discharged from these settings. In contrast, epidemic S. aureus infection has not been reported in well persons in the community. Here, we describe a group of healthy young adults who resided in the same neighborhood and participated together in school sports, and who developed serious S. aureus infections within 3 weeks of each other, suggesting a true community outbreak. Timely use of molecular epidemiological tools, however, demonstrated that their illnesses were caused by unrelated bacterial strains.

Improved recognition of MRSA case clusters by the application of molecular subtyping using pulsed-field gel electrophoresis

Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly common in hospital and community populations, making the recognition of true nosocomial outbreaks more difficult. We have used pulsed-field gel electrophoresis (PFGE) with Sma I digestion to analyse retrospectively two perceived outbreaks of epidemic methicillin-resistant Staphylococcus aureus 15 (EMRSA 15) colonization. The first cluster of cases in patients and staff on a general ward (ward D) revealed three different antibiograms based on differences in ciprofloxacin and rifampicin sensitivities. All isolates typed using PFGE, which was more discriminatory than phage-typing. One PFGE banding profile labelled type 5 was predominant, but 12 isolates proved to be subtypes of type 5 and two were PFGE type 11. Four staff members carried a strain not found in patients, three carried strains found in patients and transient carriage was highlighted as a problem when screening staff. PFGE enhanced the epidemiological data and proved that the cases on this ward did not comprise one large outbreak but numerous sporadic cases and smaller clusters. In contrast, isolates from a second cluster of cases which occurred on ward F were indistinguishable using antibiograms, phage-typing and PFGE, confirming this was more likely to be a true outbreak of colonization. We conclude that PFGE usefully augments epidemiological information and allows more logical infection control decisions to be made, with better utilization of scarce resources.

Contribution of a typing method based on IS256 probing of SmaI-digested cellular DNA to discrimination of European phage type 77 methicillin-resistant Staphylococcus aureus strains

The incidence of infections with phage type 77 methicillin-resistant Staphylococcus aureus (MRSA) strains increased in France in 1987. These strains are widespread in numerous European hospitals. The SmaI restriction profiles of total DNA extracted from 74 phage type 77 MRSA strains isolated from 1987 to 1994 in 10 hospitals in eight European cities (in France, Belgium, and Spain) were analyzed. Hybridization with a probe containing a 468-bp DNA fragment from within the transposase gene of the insertion sequence IS256 was also examined. Forty-three SmaI profiles were detected. Twenty major genotypes were identified, and each genotype contained strains with the same profile or profiles which differed by no more than three bands. Strains isolated in different countries and at several-year intervals were often grouped within the same genotype. A larger number of genotypes could be discriminated by analysis of the patterns of hybridization with the IS256 probe. SmaI restriction fragments with the same apparent electrophoretic mobility could, in some cases, be distinguished by the presence or the absence of nucleotide sequences hybridizing with IS256. The strains that grouped within the same genotype after hybridization with IS256 were mostly those isolated in the same hospital and at less than 12-month intervals. Consequently, the IS256 probe that we used improved restriction profile analysis for discrimination between the intrahospital, outbreak-related phage type 77 MRSA strains and the endemic strains disseminated in various cities and countries.

Typing of Staphylococcus aureus by PCR for DNA sequences flanked by transposon Tn916 target region and ribosomal binding site

The continuous intra- and interhospital spread of multiresistant Staphylococcus aureus demands a rapid molecular typing system. This study describes the fingerprinting of S. aureus by PCR amplification of DNA sequences flanked by the target site for transposon Tn916 and the ribosomal binding site and neighboring nucleotides (target 916-Shine-Dalgarno PCR [tar 916-shida PCR]). Both starting points for PCR are known to be randomly distributed on the S. aureus chromosome. By use of SmaI-macrorestriction patterns as the reference method it was shown that this PCR genotyping discriminates among strains of the major clonal groups of the species S. aureus (strains with phage patterns 29, +, 94, 96, and 95 as well as group II and group III patterns) and identifies the six epidemic methicillin-resistant S. aureus strains prevalent in German hospitals. All of the investigated strains including methicillin-sensitive. S. aureus were typeable. Tar 916-shida patterns are stable during the dissemination of epidemic methicillin-resistant S. aureus among different hospitals.

Discrimination of S. aureus strains by PCR for r-RNA gene spacer size polymorphism and comparison to SmaI macrorestriction patterns

The size polymorphism of the internal spacer between the 16 S and the 23 S r-RNA genes was studied in S. aureus with the aid of PCR. The patterns of corresponding PCR products were compared with SmaI-generated macrorestriction patterns for definite propagating strains of S. aureus typing phages, for strains with phage pattern 29, phage-group II patterns, phage pattern 94, 96, phage pattern 95 and epidemic methicillin-resistant strains (MRSA). The spacer length polymorphism did not prove to be as discriminative as genomic DNA fragment patterns. However, as shown for S. aureus with phage patterns 29; group II; 94, 96; 95 and also for 4 out of 6 epidemic MRSA, unique patterns of r-RNA gene spacers probably indicate a relatedness among strains which is also suggested by SmaI macrorestriction patterns.